Due to the advance of technology, the electrical appliances become smaller and lighter. Besides the size, how to efficiently reduce the power consumption without adversely effecting the operation and functions of the portable electronic apparatus is a challenge for the designer.
Please refer to FIG. 1 which is a schematic diagram illustrating a conventional high voltage regulator for use with a flashlight of a digital camera. As shown, the conventional high voltage regulator includes a transformer 100, a ringing-choke converter (RCC) 102, a rectifying diode 104, a capacitor C, a comparator 106, a micro-processor 108 and an AND gate 110. The primary winding of the transformer 100 includes two input endpoints and one inter-tapping end. The inter-tapping end and one of the input endpoints are connected to the RCC 102 and the other input endpoint is connected to a power source voltage (Vs). One end of the secondary winding of the transformer 100 is grounded and the other end is connected to one end of the rectifying diode 104. The capacitor C is connected between the other end of the rectifying diode 104 and ground so that a rectification circuit is formed between the rectifying diode 104 and the capacitor C. As shown in FIG. 1, two resistors R1 and R2 are connected to each other in series and the combination thereof is further connected to the capacitor C in parallel. The negative electrode of the input end of the comparator 106 is connected between two resistors R1 and R2 while the positive electrode of the comparator 106 is connected to a reference voltage (Vref). The output end of the comparator 106 is connected to the micro-processor 108 and one input end of the AND gate 110. The other input end and the output end of the AND gate 110 are connected to the micro-processor 108 and the RCC 102, respectively.
When the high voltage regulator starts operating, there is no voltage in the capacitor. The positive electrode of the input end of the comparator 106 has a voltage larger than that of the negative electrode, so as to output a high level from the comparator 106 to the micro-processor 108 and the AND gate 110. After receiving the high level, the micro-processor 108 provides another high level to the AND gate 110. Since both input ends of the AND gate 110 receive the high level, the output end of the AND gate 110 outputs the high level to the RCC 102.
Once receiving the high level, the RCC 102 starts to oscillate for generating a pulse signal from the center-trap of the primary winding of the transformer 100. The duty cycle of the pulse signal is smaller at first, gradually increases, and then reaches a stable status after a certain period. When the pulse signal goes to the primary winding of the transformer 100, the secondary winding of the transformer 100 generates an induced current. Thus, the capacitor C starts to be charged via the operation of the rectifying diode 104. When the capacitor C is charged to a certain voltage, e.g. 330V, the certain voltage is divided by the resistors R1 and R2, and compared with the reference voltage Vref in the comparator 106 so as to output a low level to one input end of the AND gate 110. Then, the output end of the AND gate 110 outputs the low level to stop the oscillation of the RCC 102. At this time, the capacitor C finishes the charge ready for the flashlight.
Besides the flashlight, other devices of a digital camera, e.g. a liquid crystal display (LCD), may also consume much power. Hence, the conventional digital camera is not able to switch on the LCD and actuate the high voltage regulator of the flashlight at the same time. In other words, the LCD is not able to be turned on until the capacitor C is fully charged and the micro-processor 108 stops the operation of the high voltage regulator of the flashlight. Then, the user can focus the camera and take a photo.
The current leakage, however, is always a problem for an electric apparatus, and so is for a digital camera. If it takes too much time to focus the digital camera after the capacitor is fully charged, the voltage of the capacitor will largely drop because of the current leakage. At this moment, the micro-processor 108 interrupts and stops the focusing operation. That is, the LCD is shutdown and the high voltage regulator of the flashlight is re-started. It is necessary to wait the capacitor to be fully charged, the user can focus the digital camera again. Since it consumes a lot of power to restart the RCC 102, the conventional digital camera cannot simultaneously bear the power required by the LCD and the high voltage regulator of the flashlight.
Moreover, when the RCC 102 reaches a stable status, the pulse signal has a fixed duty cycle. It has no way to control the RCC 102 to change the duty cycle of the pulse signal in the conventional digital camera.
Therefore, the purpose of the present invention is to develop a high voltage regulator and a method for regulating a voltage to deal with the above situations encountered in the prior art.